Stopping the movement of water towards the foundation depends on two straight-forward concepts: 1) Water flows down hill, that is, water flow is directed by gravity; and 2) water will take the path of least resistance. In our experience, many basement and foundation problems can be traced to a discharging down spout, a broken rain gutter, or a leaky sprinkler head or spigot, and a simple repair may solve the problem. Sometimes the movement of water towards a foundation is the result of obvious slope and ground surface features, and the owner, possibly with the help of a landscaping contractor, might be able to re-direct water flow away from the foundation with basic landscaping improvements.
Dealing with more serious drainage and foundation issues, however, requires identifying problem soils and both surface and underground-channel ways for water flow. Too often, solutions to wet basements and cracked foundations are proposed based only on visual examination by contractors promoting their own product or procedure. What is actually required is a comprehensive engineering evaluation with test borings to characterize soils and identify subsurface channel ways for water flow, and a structural analysis of the condition of the foundation and the rest of the house.
Evaluating foundation soils and the movement of water around and below a basement or structure is the area of expertise of a geotechnical engineer. One of our roles as the geotechnical engineer “investigator” is to help figure out the most cost effective method to keep water away from a house. When necessary, we also determine the most economical way to stabilize and repair foundations and walls that have cracked or settled. Installing an expensive foundation drainage system or repairing a settling or cracked foundation without the input of a geotechnical engineer is like having surgery performed without X-rays or blood tests.
The number of possible sources of intruding water is mind boggling. For example, water discharging from rain gutters and downspouts may be flowing back towards a house. Now may be a good time to take a look and make sure that the ground surface slopes properly away from your house! Chances are that foundation drains are present around your home, but unless they were installed properly, pipe perforations and the surrounding gravel blanket are very likely to have clogged over the years. If water is getting into your basement, it might mean that your foundation drains are no longer functioning properly.
Several of our recent projects provided good illustrations of the need to take into account the complex relationship of soil characteristics, the structures on the site, and the overall “lay of the land” in order to figure out the best way to solve water intrusion and foundation problems. In one unusual project, we were called to investigate drainage and structure problems at a house with extensive cracking of the basement slab, severely cracked driveway, sink holes in the front yard, and a history of water intrusion into the basement that lead to the installation of an expensive drain system below the basement slab. In the midst of this nightmare scenario, we were surprised that the garage slab seemed to be in good condition. When we brought this up to the homeowner, we were informed that the garage slab had been refinished fairly recently by a company that had also pumped grout below the slab to prevent further settlement and cracking. The only problem was that the garage slab still seemed to be settling.
We were able to help the frustrated home owner by designing an effective drainage system outside the house. We helped identify the most suitable location and depth of the drains, helped to determine the best way to deal with the discharge from the drain system, and provided guidance in crack repair and water- proofing of the foundation walls. Successful replacement of the cracked driveway and stabilization of the garage slab were cost effectively undertaken with minimal disturbance to the property grounds by incorporating effective earthwork procedures with proper structural support measures. The final step of the project was the repair of sink holes and improvement of site grading to assure the movement of water safely away from the house during rain storms.
Although it is sometimes more cost effective to deal with wet basement issues from the interior of the house, it is always worth trying to identify the outside sources of the water and cut the flow of water off before it can enter the house. Exterior grading and drainage control measures will greatly reduce the likelihood of foundation settlement or other serious structural problems. If installing drains below the basement floor slab is the only feasible way to tackle the wetness issue, soil test borings and geotechnical analysis will greatly help to identify the best location, depth and design features for the system. After all, who would want surgery without a comprehensive examination before hand?
Copyright 2011 Daniel A. Freiberg, PE, PG